Rotor short-circuiting switch

Abstract

A transistor switch short-circuits the main field rotor winding of a synchronous machine during start-up. A transistor is connected across the main field rotor winding and is responsive to the polarity of the voltage induced in the main field rotor winding by the main stator winding. When the voltage is of one polarity, the transistor conducts to short-circuit the main field rotor winding. When the voltage across the main rotor winding is of the opposite polarity, diodes limit the voltage buildup. The transistor which shorts the main field rotor winding is rendered inoperative when the machine is operating at or near synchronous speed.

I claim: 
     
       1. In a synchronous machine having a main stator winding, an exciter field winding, and a rotor on which is mounted a main field rotor winding and an exciter armature winding, an improved circuit for shorting the main field rotor winding comprising: a transistor for shorting the main field rotor winding when the voltage across the main field rotor winding is of one polarity;   diode means for limiting the voltage across the main field winding when the polarity of the voltage across the main field rotor winding is of the other polarity; and   means for rendering the transistor inoperative when a voltage is received from the exciter armature.   
     
     
       2. The synchronous machine of claim 1 wherein the transistor has a base, emitter and collector, the emitter and collector connected across the main field rotor winding, the improved circuit further including: a second transistor having a base, emitter and collector, the collector and the emitter of the second transistor connected between the base and the collector of the first transistor, the base of the second transistor connected to said means for rendering the transistor inoperative.   
     
     
       3. The synchronous machine of claim 1 wherein the transistor has a base, emitter and collector, the emitter and collector are connected across the main field rotor winding; and the base is coupled to said means for rendering the transistor inoperative.   
     
     
       4. The synchronous machine of claim 1 wherein the means for rendering the transistor inoperative include: diode means coupled to the exciter armature winding; and   a first and a second resistor connected in series between the diode means and the main field rotor winding.   
     
     
       5. The synchronous machine of claim 1 wherein the diode means are connected in series with the main field rotor winding and the exciter armature winding. 
     
     
       6. In a synchronous machine having a main stator winding, an exciter field winding, and a rotor on which is mounted a main field rotor winding and an exciter armature winding, an improved circuit for shorting the main field rotor winding comprising: a first transistor having a base, emitter and collector, the emitter and collector connected across the main field rotor winding;   a second transistor having a base, emitter and collector, the emitter and the collector of the second transistor connected between the collector and the base of the first transistor;   a first, second and third diode each connected in series with the exciter armature winding and the main field rotor winding;   a first resistor connected between the main field rotor winding and the base of the second transistor; and   a second resistor coupled between the base of the second transistor and a fourth, fifth and sixth diode, each of which is coupled to the exciter armature winding.   
     
     
       7. In a synchronous machine having a main stator winding, an exciter field winding, and a rotor on which is mounted a main field rotor winding and an exciter armature winding, an improved circuit for shorting the main field rotor winding comprising: a transistor having a base, emitter and collector, the emitter and the collector connected across the main field rotor winding;   a first and a second set of three diodes connected in series between the main field rotor winding and the exciter armature winding;   a first resistor connected between the base and the collector of the transistor;   a second resistor coupled to a third set of three diodes, each of which is connected to the exciter field winding; and   a fourth set of three diodes, each diode connected in series between the main field rotor winding and the exciter armature winding.